Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo2O5+d Double Perovskite

Abstract

Abstract:The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometryand electrical conductivity in layered LaBaCo2O5`δdouble perovskite was studied as a function oftemperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo2O5`δdouble perovskite was obtained by annealing cubic A-site cation disordered La0.5Ba0.5CoO3 ́δperovskite at 1100 ̋C in N2. High temperature X-ray diffraction between room temperature (RT) and800 ̋C revealed that LaBaCo2O5`δremains tetragonal during heating in oxidizing atmosphere, butgoes through two phase transitions in N2and between 450 ̋C and 675 ̋C from tetragonalP4/mmmtoorthorhombicPmmmand back toP4/mmmdue to oxygen vacancy ordering followed by disorderingof the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo2O5`δwasdemonstrated. La0.5Ba0.5CoO3 ́δremained cubic at the studied temperature irrespective of partialpressure of oxygen. LaBaCo2O5`δis metastable with respect to La0.5Ba0.5CoO3 ́δat oxidizingconditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Coin the two materials. The oxidation state of Co is higher in La0.5Ba0.5CoO3 ́δresulting in a higherelectrical conductivity relative to LaBaCo2O5`δ. The conductivity in both materials was reducedwith decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior.